Rename Django's dev branch to main. (#746)

More information: https://groups.google.com/g/django-developers/c/tctDuKUGosc/
Refs: django/django#14048

.github/workflows/test.yml

@@ -10,7 +10,7 @@ jobs:
       fail-fast: false
       matrix:
         python-version: ['3.6', '3.7', '3.8', '3.9', 'pypy3']
-        django-version: ['2.2', '3.0', '3.1', 'dev']
+        django-version: ['2.2', '3.0', '3.1', 'main']
 
     steps:
     - uses: actions/checkout@v2

tox.ini

@@ -1,7 +1,8 @@
 [tox]
 envlist =
   pypy3-dj{22,30,31}
-  py{36,37,38,39}-dj{22,30,31,dev}
+  py{36,37,38,39}-dj{22,30,31}
+  py{38,39}-djmain
   docs
 
 [gh-actions]
@@ -17,7 +18,7 @@ DJANGO =
     2.2: dj22
     3.0: dj30
     3.1: dj31
-    dev: djdev
+    main: djmain
 
 [testenv]
 basepython =
@@ -31,7 +32,7 @@ deps =
   dj22: Django>=2.2.1,<2.3
   dj30: Django>=3.0,<3.1
   dj31: Django>=3.1,<3.2
-  djdev: https://github.com/django/django/archive/master.tar.gz
+  djmain: https://github.com/django/django/archive/main.tar.gz
   jinja2
   coverage
   jsmin==2.2.0
@@ -48,9 +49,9 @@ commands =
     {envbindir}/coverage xml
 whitelist_externals = npm
 ignore_outcome =
-    djdev: True
+    djmain: True
 ignore_errors =
-    djdev: True
+    djmain: True
 
 [testenv:docs]
 basepython = python3.8